The conversion of methyl alcohol or dimethyl ether into open chain hydrocarbons of the gasoline range, as well as of cyclic aromatic nature, is of recent substantial significance in the context of the utilization of inexpensive starting materials, which can be produced from a variety of sources, including coal, wood products, natural gas or other sources of methane gas, including any source of bio-mass.
A century ago, LeBel and Greene first reported (Beilstein, Vol. 1, p. 277 (1918)) the production of gaseous saturated hydrocarbons (and some hexamethylbenzene) by adding methyl alcohol dropwise to "hot" zinc chloride. Grosse in U.S. Pat. No. 2,492,984 described the formation of hydrocarbons from methyl alcohol over zinc chloride at 400.degree. to 425.degree. C. and pressures ranging from 1,000 to 2,500 psi. Kim et al. recently reported (J. Org. Chem., 43, 3432 (1978)) that when methyl alcohol was reacted with a large excess of zinc iodide or bromide at 200.degree. C. under 200 psi of nitrogen, a mixture of C.sub.4 to C.sub.13 hydrocarbons containing almost 50% of 2,2,3-trimethylbutane (triptane) was obtained. This unusual selectivity was considered to be the consequence of a carbenoid-type mechanism involving organozinc (Simmons-Smith type) complexed carbene intermediates.
The conversion of dimethyl ether mixed with "a normally gaseous alkane generally isobutane" over a silica-alumina catalyst at 350.degree. to 400.degree. C. and 10-800 psi has been reported in U.S. Pat. No. 2,456,584; a mixture of normally liquid hydrocarbons, predominantly of the isoparaffinic and aromatic types, was obtained.
Supported aluminum sulfate has also been used for the conversion of methyl alcohol and dimethyl ether into higher hydrocarbons by contacting them at 250.degree. to 400.degree. C. as described in U.S. Pat. No. 4,072,733. The overall conversion was, however, low.
Alcohols of two or more carbon atoms produce a variety of hydrocarbons using polyphosphoric acid or other dehydrating agents at elevated temperature and pressure, as described for example in U.S. Pat. No. 2,373,475.
Pearson in U.S. Pat. No. 4,133,838 describes the conversion of methyl alcohol or trimethyl phosphate to hydrocarbons using phosphorus pentoxide or polyphosphoric acid in molar quantity as condensing agent. A wide range of hydrocarbons (about 200 compounds) are formed in 36 to 39% yield. The transformations have been explained by .beta.-elimination followed by condensation or polymerization of the olefin to higher hydrocarbons.
The Mobil Oil Company in recent years disclosed a new type of shape selective catalytic processes using the acidic form of a particular type of alumino-silicate molecular sieve catalysts called ZMS-zeolites, such as ZMS-5 as described in U.S. Pat. No. 3,702,886, for the conversion of methyl alcohol into gasoline-range hydrocarbons. The process has been described in a number of patents, such as U.S. Pat. Nos. 3,894,106, 3,894,107, 3,928,483. The key to the process is stated to be the favorable shape selectivity of the catalyst allowing zeolite conversion to take place in the cavities and channels of intermediate pore size. For example, Chang and Silvestri in the J. Catalysis, 47, 249 (1977) described in detail the overall shape selective Mobil conversion of methyl alcohol into hydrocarbons, proposing a carbenoid-type mechanism to account for the initial step of the overall process. Derouane et al. elucidated other aspects of the mechanism using .sup.13 C NMR studies, proposing a propagating carbocation mechanism to explain most of the products obtained (J. Catalysis, 53, 40 (1978).
The ZMS-5 technology disclosed by Mobil originally was for the production of liquid hydrocarbon mixtures of the gasoline range; subsequently, as described in U.S. Pat. No. 3,911,041, a modified zeolite catalyst containing phosphorus incorporated within the crystal structure, was described as producing from methyl alcohol or dimethyl ether products rich in olefins. These catalysts were also further modified by impregnation with zinc. Similar results were described with manganese impregnated zeolites as in DOS No. 2,755,229 (1979, Hoechst).